Sounds like a lot of scraping and wire brush work. What about some paint remover?? Maybe try some on a small area. Have you tried a high heat burn to see if it would peel some?? If it wouldn't peel, at least the volatiles in the paint would get cooked off. Good Luck!!
Compliments on the creative use of the frozen water in your pan for lowering the temp. Gives others in some of the little more warmer areas a chance to try smoking some cheese.
You're going to love the 14.5. I use ours more than the 18.5 and 22.5. Holds temps great and the size of the grate allows me to clean it in our kitchen sink unlike the other two wsm's!!
My kettles and wsm's are stored with vents open, outside, using Weber covers, damp here in the winter but they don't seem to get any mould on the grills or inside the cookers.